The present invention relates to methods of recovering multi-rater printed circuit boards, and more particularly to a method of recovering a multi-layer printed circuit board by recovery of defective through holes in the circuit board.
For example, a multi-layer printed circuit board on which many electronic parts are mounted when an electronic computer system is constructed has recently been required to increase in density and the number of layers. Therefore, the circuits formed on the board become denser and the spacings between the formed through holes and the circuit patterns on the inner layer have more and more been reduced.
If a small foreign matter of metal intervenes at a position on a multi-layer printed circuit board where the through hole is provided, those through holes and other circuits are put in a short-circuited state. Under such situation, such board cannot be used and must be dumped as a bad one, which is one of the causes which reduce a yield in the process of manufacturing such boards.
In order to prevent a decrease in the yield of such circuit boards, for example, JP-A 62-186597 discloses a recovering method of cutting a defective through hole into a through hole having a predetermined diameter, providing a conductor which extends through a solid resin along the through hole, and connecting circuits provided on each end of the conductor and on each of the opposite surfaces of the multi-layered printed board to thereby form a through hole circuit.